Single point hinge for a container

ABSTRACT

A single point hinge and a method of thermoforming a plastic container including a single point hinge include a lid, a tray, a single point hinge connecting the lid and the tray. The single point hinge includes an angle formed by a lid chamfer and a tray chamfer. The single point hinge further includes a lid well adjacent to the lid chamfer and a tray well adjacent to the tray chamfer, and the lid connects to the lid well and the tray connects to the tray well.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a continuation of application Ser. No. 10/641,671,filed Aug. 15, 2003. The entire content of that application isincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM ON COMPACT DISC

Not applicable.

FIELD OF INVENTION

The present invention relates to a single point hinge for plasticcontainers and a method of manufacturing the single point hinge.

BACKGROUND OF THE INVENTION

Restaurant and food-related industries demand plastic containers forfood storage and transportation that are economical to purchase,effective in preserving food, effective in containing the food and itsrelated moisture, attractive to the consumer, and easy to operate. Oneof the most important features for hinged plastic containers is thehinge design, which is critical to many of the above-describedperformance characteristics.

Prior art hinge designs include a “box hinge” shown in FIG. 1(A), a “W”hinge shown in FIG. 1(B), a two-point hinge shown in FIG. 1(C), athree-point hinge shown in FIG. 1(D), and a cylindrical hinge shown inFIG. 1(E). These prior art hinges are unacceptable for many reasons. Forexample, the box hinge is difficult to thermoform with its many sharpangles. And, due to the draw ratio of the box hinge, the resulting boxhinge is often malformed. It is also often difficult to form a box hingeusing polypropylene, a plastic material preferred in many plasticcontainer applications.

The “W” hinge is difficult to consistently form owing to its many sharpangles. The depth of the “W” hinge is larger than the width of either ofits side portions. The “W” hinge may also retain too much “memory” andmay tend to close by itself. The memory of plastic containers refers tothe inherent tendency of the plastic container to return to itsdetermined position. For example, a container with too much memory maytend to automatically close when opened, much to the disgust of the enduser, who could be attempting to remove the contents of the container oreat from the container. It is preferred that a container, once opened,will remain opened, and that a container, once closed, will remainclosed.

The two-point and three-point designs are also more difficult toconsistently form during manufacturing as they have multiple compressionpoints. A complicated manufacturing process results in a higherpercentage of product not meeting quality specifications or consumerexpectations.

The more complicated hinge designs, such as the two-point, three-point,and “W” are difficult to form consistently. Many plastic containers aremade by a thermoforming process, which only allows a few seconds to formthe hinge. Thus, it is imperative that the hinge may be quickly andaccurately formed.

The cylindrical hinge shown in FIG. 1(E) involves a coining processduring manufacturing. The manufacturing of the cylindrical hingeinvolves a coining process. Coining processes generally involve thethinning of a plastic material at desired location(s). The coining ofthe cylindrical hinge may be accomplished using the compression forcesupplied by the forming press. If the cylindrical hinge is squeezed toomuch, a weakened, overly coined area may result in the hinge and causeproduct failure, i.e., the lid of the container tears away from the trayof the container at the hinge. Previous attempts to improve themanufacturing process of the cylindrical hinge have incorporated arevised cylindrical shape that leaves areas of a thicker plasticmaterial along the coined region for reinforcement. The coined region ofthe cylindrical hinge is shown by reference numeral 2 and thereinforcing region is shown by reference numeral 4.

Other disadvantages of prior art hinges include poor closure of thecontainer near the hinge. Poor closure of the container may result inleakage. The closure of the container near the hinge is especiallysusceptible to poor closure due to the physical proximity of the hingeto the locking profile of the container.

Another disadvantage of the prior art involves “narrow” windows forprocess operation. Many prior art containers require exactingspecifications that may prove difficult for the manufacturer toeconomically meet and may result in considerable waste due tounacceptable product.

SUMMARY OF THE INVENTION

The present invention is directed to a plastic container with a singepoint hinge and a method of thermoforming both the plastic container andthe single point hinge. The plastic container may include a lid, a tray,and a single point hinge that connects the lid and the tray. The singlepoint hinge includes an angle formed by a lid chamfer and a traychamfer. The single point hinge further includes a lid well adjacent tothe lid chamfer and a tray well adjacent to the tray chamfer. The lidconnects to the lid well, and the tray connects to the tray well.

Aspects of the present invention resulting in advantages over the priorart include:

The present invention provides a hinge for a plastic container thatprovides positive closure. The single point hinge of the presentinvention is easier to manufacture than many prior art hinges.

The single point hinge is easy to form consistently as the processwindow is opened to a wider range of tolerances resulting in increasedflexibility in the manufacturing process.

The single point hinge helps clear interference near the hinge andpromotes secure closing.

The single point hinge requires less manufacturing steps than many priorart hinges.

The single point hinge exhibits a lack of memory that is preferred byconsumers. A lid incorporating a single point hinge will tend to stayopen or closed depending on which side of 90° (i.e., halfway betweenopen and closed) the lid is located.

These and other aspects of the present invention are achieved herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A) shows an example of a “box” hinge.

FIG. 1(B) shows an example of a “W” hinge.

FIG. 1 (C) shows an example of a two-point hinge.

FIG. 1(D) shows an example of a three-point hinge.

FIG. 1(E) shows an example of a cylindrical hinge.

FIG. 2 shows a perspective view of a plastic container incorporating thesingle point hinge of the present invention.

FIG. 3 shows a top down view of the plastic container, in an openposition, incorporating the hinge of the present invention.

FIG. 4 shows a side view of the plastic container, in an open position,incorporating the single point hinge of the present invention.

FIG. 5 shows a perspective view of the single point hinge of the presentinvention.

FIG. 6 shows a side view of the single point hinge of the presentinvention.

FIG. 7(A) is a close-up view of the single point hinge of the presentinvention.

FIG. 7(B) is a close-up view of the single point hinge of the presentinvention with some corners forming radii.

FIG. 8(A) shows the single point hinge of the present invention in a“closed position.”

FIG. 8(B) shows the single point hinge of the present invention withradii comers in a “closed position.”

FIGS. 9(A)-(E) show a closing of the hinge of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a plastic container with a singepoint hinge and a method of thermoforming both the plastic container andthe single point hinge. The plastic container may include a lid, a tray,and a single point hinge that connects the lid and the tray. The singlepoint hinge includes an angle formed by a lid chamfer and a traychamfer. The single point hinge has a thinned region at the angle formedby the lid chamfer and the tray chamfer. The single point hinge furtherincludes a lid well adjacent to the lid chamfer and a tray well adjacentto the tray chamfer. The lid connects to the lid well, and the trayconnects to the tray well. The lid well and the tray well assist thesingle point hinge to function properly by inhibiting interference fromother parts of the plastic container or the single point hinge itself.

In one embodiment of the present invention, the lid well and the traywells may each include a horizontal surface substantially perpendicularto two vertical surfaces. The vertical surfaces of the lid well and traywell are substantially parallel to each other. The horizontal surface isconnected to the two vertical surfaces and is in between the twovertical surfaces. In a preferred embodiment, the horizontal surface islonger than either of the two vertical surfaces.

In another embodiment of the present invention, the corners between thehorizontal surfaces and vertical surfaces of the lid well and tray wellsform radii.

In another embodiment of the present invention, the vertical surfaces ofthe lid and tray wells are at angle of approximately 75° toapproximately 105° to the horizontal surface of the lid and tray wells.

The lid, tray, and the single point hinge may be thermoformed from thesame sheet of plastic material. The single point is formed by the twochamfers in the thermoforming process. The single point forms an anglebetween the two chamfers. A region around the single point is alsothinned during the thermoforming process to a thinner thickness than theremainder of the plastic material.

A single point hinge of the present invention may be used in a plasticcontainer such as the plastic container shown in FIGS. 2-4. Of course,the present invention is not limited to the plastic container shown inthe FIGURES. The single point hinge of the present invention

Turning to FIGS. 2-4, a plastic container 6 includes a tray 8 and a lid10. The tray 8 and the lid 10 are connected by a hinge 12 across a lidtrim flange 30 and a tray trim flange 32. Typically, the plasticcontainer 6 is formed by thermoforming, and the tray 8, the lid 10, andthe hinge 12 are made from one sheet of plastic material.

The tray 8 defines a cavity 14 for containing food items. Fill lines 16in the tray 8 may conveniently show volumetric measurements in thecavity 14.

The lid 10 and the tray 8 may be securely closed by interlocking afemale locking rim 18 and a male locking rim 20.

A vent 22 provides for the venting of steam to maintain fried food itemscrisp and to prevent the saturation of other food items from containedmoisture. The vent 22 also reduces the likelihood of over-expansion ofthe plastic container 6 during heating. Depressions 24 in the tray 8 mayalso interlock with protrusions 26 on the lid 10. This interlockingarrangement improves the stackability of the plastic container 6 withanother plastic container. The arrangement of the depressions 24 andprotrusions 26 also allow for venting through vent 22 even when plasticcontainer 6 is in a stacking arrangement with other plastic containers.

Turning now to FIGS. 5-7, an example of a single point hinge of thepresent invention is shown. The single point hinge 12 connects the tray8 and the lid 10. The term “connects” as used herein refers to thejoining of the tray 8 and the lid 10 by an integral section of plastic,i.e., one piece of plastic. The tray 8, the lid 10, and the hinge 12 aregenerally made from the same sheet of plastic material and are notjoined or attached together from several independent pieces of plastic.Instead, the tray 8, the lid 10, and the hinge 12 are thermoformed fromthe same sheet of plastic in molds.

The single point hinge includes a hinge point 40. A lid chamfer 42 and atray chamfer 44 are adjacent to the hinge point 40. A point angle 41 isformed between the lid chamfer 42 and the tray chamfer 44. The pointangle 41 may range from approximately 60° to approximately 120°. In apreferred embodiment, the point angle 41 is approximately 90°. Hingeoperation will be less dependable outside of either range.

A lid vertical portion 38 is connected to the lid chamfer 42. A trayvertical portion 39 is connected to the tray chamfer 44. The lid andtray vertical portions 38, 39 and the chamfers 42, 44 substantiallydefine a point space 49 that is evident when the hinge 12 is in an“open” position. An outline of the point space 49 is somewhat in theshape of a triangle (formed by the chamfers 42, 44) on the top of asquare (formed by lid and tray vertical portions 38, 39).

A lid well 46 and a tray well 48 are formed on both sides of the pointspace 49. The lid well 46 is formed by the lid vertical portion 38, alid horizontal well portion 50 and a lid vertical well wall 54. A traywell 48 is formed by the tray vertical portion 39, a tray horizontalwell portion 52, and a tray vertical well wall 56. The horizontal wellportions 50 and 52 are generally longer that either the verticalportions 38, 39 or the vertical well walls 54, 56. It is preferred thatthe vertical well walls 54, 56 have an angle of approximately 75° toapproximately 105° to the horizontal well portions 50, 52. In a mostpreferred embodiment, the vertical well walls 54, 56 have an angle ofapproximately 90° to the horizontal well portions 50, 52.

In a preferred embodiment, the lid trim flange 30 and the tray trimflange 32 are substantially parallel to the horizontal well portions 50,52.

A lid well transition 58 and a tray well transition 60 connect to thelid and tray vertical well walls 54 and 56, respectively. The lid welltransition 58 and the tray well transition 60 connect to the lid trimflange 30 and the tray trim flange 32 at a lid trim transition point 62and a tray trim transition point 64.

The lid trim flange 30 and the tray trim flange 32 generally form aflange angle 72 of approximately 15° to approximately 25° to the lidwell transition 58 and the tray well transition 60. In a most preferredembodiment the flange angle 72 is approximately 15°.

FIGS. 7(A) and 8(A) show a single point hinge of the present inventionin an “opened” and “closed” position. The single point hinge of FIGS.7(A) and 8(a) show an embodiment with some corners forming radii.

FIGS. 7(B) and 8(B) shows a single point hinge of the present inventionin an “opened” and “closed” position.

The closed hinge in FIGS. 8(A) and 8(B) substantially closes about thehinge point 40. The hinge point 40 is generally the only hinging region.Of course, other angled regions of thermoplastic material will flex andbind under a load.

As can be seen in FIGS. 8(A), 8(B), and 9(A)-(E), the lid well 46 andthe tray well 48 provide clearance for the hinge 12 to close and toprevent the touching of the chamfers 42, 44 or other hinge components.The hinge 12 closes such that only the lid trim flange 30 and the traytrim flange 32 are in contact. The touching of the chamfers or otherhinge components may prevent proper closure or prevent the opened lidand tray from lying in a substantially flat position.

The lid vertical portion 38 and the tray vertical portion 39 may beapproximately 0.040-0.080 inches apart for certain containers generallyused by consumers. In a most preferred embodiment, the distance betweenthe lid vertical portion 38 and the tray vertical portion 39 isapproximately 0.060 inches.

The distance from the point hinge 40 to the bottom of the point space 49is approximately 0.035-0.085 inches. In a preferred embodiment forconsumer use, the point space is approximately 0.065 inches.

The plastic container incorporating the hinge of the present inventionmay be made from a variety of thermoplastics. It is preferred that theplastic is capable of heat forming and, after forming, the plastic willtolerate temperatures of approximately 240° Fahrenheit. The single pointhinge of the present invention is intended to be microwave safe for thewarming and heating of foods.

Thermoplastics for use with the single point hinge of the presentinvention include polyolefins such as polypropylene and polyethylene.

Preferred polypropylenes include random copoly polypropylene, copolypropylene, and homo polypropylene. It is preferred that thethermoplastic used in conjunction with the present invention have a meltflow range of approximately one to approximately five grams per tenminutes at 230° Celsius.

Preferred thermoplastics have a thickness of approximately 0.025 inchesto approximately 0.040 inches, although thicker and thinnerthermoplastics may be used with the single point hinge of the presentinvention.

The manufacturing of containers incorporating the hinge of the presentinvention involves thermoforming. The exact methods and details ofthermoforming plastic containers are well known to one of ordinary skillin the art and need not be repeated in the present disclosure.Nonetheless, thermoforming generally involves the heating of theplastic, the molding of the plastic, the cooling of the plastic and thetrimming of the plastic. The molding process may incorporate molddesigns well known to those skilled in the art of thermoformingplastics. Typically a sheet of the plastic material, such aspolypropylene, is heated and fed into the mold where the containers areformed by using vacuum, form air, and assist plugs to move the plasticagainst the forming surfaces for the forming cavity.

During the thermoforming of the single point hinge of the presentinvention, the plastic material may be heated to approximately 300°Fahrenheit before molding. During the molding process that forms thesingle point hinge of the present invention, a region of the hinge 12 atthe hinge point 40 is thinned by a coining process or other thinningprocesses well known to one of ordinary skill in the art. This thinnedregion 70 is on the point space 49 side of the hinge 12. The coiningprocess may incorporate the use of springs to provide the coiningpressure. A particularly preferred spring is a Bellville™ spring. Thesprings provide for control of the amount of coining force applied by acoining anvil. At the hinge point 40, the plastic material in thethinned region 70 may be coined to approximately 0.003 inches toapproximately 0.008 inches.

The single point hinge of the present invention maintains closure of themale locking rim and female locking rim in the area adjacent to thesingle point hinge. The single point hinge provides positive closurewithout the interference from portions of the hinge.

Unlike many perforated hinges, the single point hinge is durable and notprone to separation failure as some perforated hinges will tend tobreak. In the single point hinge, the only portions of the hinge thatare touching each other are the lid trim flange and the tray trimflange. This reduces the likelihood for interference at the hinge.

The single point hinge of the present invention provides for a largerrange of tolerances in the manufacturing process than many prior arthinge designs. This reduces the rejects that fail the manufacturingspecifications. The single point hinge design is easier to manufacturesince there are less angles than many other conventional hinges.

The terms “vertical” and “horizontal” have been used for purposes ofgeneral orientation and are not intended for absolute guidance, as itwill be understood by one of ordinary skill in the art that it is therelative relationships between walls ands surfaces that are beingdescribed and not limited to a fixed vertical and horizontalorientation.

The materials forming the single point hinge and embodiments of thepresent invention may “relax” after the original thermoforming processinto shapes approximating embodiments that are equivalents of theembodiments described and claimed herein. Moreover, through extendeduse, materials forming the single point hinge and embodiments of thepresent invention may be altered into equivalents of the embodimentsdescribed and claimed herein.

As is evident from the foregoing description, certain aspects of thepresent invention are not limited by the particular details of theexamples illustrated herein, and it is therefore contemplated that othermodifications and applications, or equivalents thereof, will occur tothose skilled in the art. It is accordingly intended that the claimsshall cover all such modifications and applications that do not departfrom the spirit and scope of the present invention.

1. A plastic container, comprising: a lid; a tray; a hinge connectingthe lid and the tray; and the hinge comprising: an angle formed by a lidchamfer and a tray chamfer; a lid well adjacent to the lid chamfer and atray well adjacent to the tray chamfer; and wherein the lid connects tothe lid well by a lid well transition and the tray connects to the traywell by a tray well transition.
 2. The plastic container according toclaim 1, further comprising: a tray flange that connects the hinge tothe tray; a lid flange that connects the hinge to the lid; and whereinthe closure of the hinge results in contact between the lid flange andthe tray flange.
 3. The plastic container according to claim 1, whereinno other portion of the hinge is in contact with another portion of thehinge except the contact between a lid flange and a tray flange.
 4. Theplastic container according to claim 1, wherein the angle isapproximately 60° to 90°.
 5. The plastic container according to claim 1,wherein the angle formed by the lid chamfer and the tray chamfer resultsin a hinge point.
 6. The plastic container according to claim 8, whereina thermoplastic material that forms the hinge point is thinned orcoined.
 7. The plastic container according to claim 9, wherein thethermoplastic material at the hinge point is thinned or coined toapproximately 0.003 inches to approximately 0.008 inches.
 8. The plasticcontainer according to claim 1, wherein the plastic is random copolypolypropylene, copoly propylene, or homo polypropylene.
 9. The plasticcontainer according to claim 1, where the hinge has as a single hingepoint.
 10. The plastic container according to claim 1, wherein the hingegenerally has a single point around which the hinge closes.
 11. Aplastic container, comprising: a lid thermoformed from a sheet ofplastic material; a tray thermoformed from the sheet plastic material; ahinge thermoformed from the sheet plastic material, the hinge connectsthe lid and the tray; and the hinge comprising: a single point formed bytwo chamfers thermoformed from the sheet of plastic material; the singlepoint forming an angle between the two chamfers; and wherein thethermoformed plastic material is thinner at the single point than theremainder of the plastic material.